Effect of melittin from Apis mellifera venom on bronchogenic carcinoma cell proliferation and tumor-associated macrophage differentiation

Bronchogenic carcinoma or lung cancer is the most leading cause to death nowadays. Although paclitaxel extracted from Taxus brevifolia (Pacific yew) has commonly used as drug to treat lung cancer patients, drug resistance has become a serious problem. Thus, an alternative anti-cancer drug is challenging. Here, melittin, a water-soluble toxic peptide, from Apis mellifera venom, is the interest. Due to the half maximum concentration from MTT assay, melittin was more cytotoxic to human bronchogenic carcinoma cells (Chago K-1) than human lung fibroblasts (CRL-1947) as normal control cells. By annexin V and propidium iodide staining and flow cytometry analysis, melittin could induce Chago K-1 to undergo apoptosis. In addition, it caused the cell cycle arrest of only Chago K-1 at S phase. To investigate tumor microenvironment which directly affects the survival of cancer cells, the activation of circulating monocytes (THP-1) to differentiate into tumor-associated macrophages (TAMs) was investigated. By sandwich-ELISA used to measure interleukin-10, a molecule secreting out of TAMs, the result showed that melittin could inhibit the differentiation of THP-1 into TAMs. Since cathepsin S (cat S) is significantly involved with the severity of cancer in term of proliferation, migration and angiogenesis, here, the expression of cat S was observed by quantitative RT PCR. It was found that the expression of cat S was decreased in melittin treated Chago K-1. Also, by flat plate colony formation assay to observe cell proliferation and migration, melittin could reduce the number of colonies forming in Chago K-1 cells, comparing to untreated cells. However, by ELISA assay for secretion of vascular endothelial growth factor (VEGF), melittin could not affect angiogenesis of Chago K-1. In conclusion, melittin could induce apoptosis and arrest the cell cycle of Chago K-1. Furthermore, it could inhibit the differentiation of THP-1 into TAMs and decrease the expression of cat S.